Shadow mask support mechanism for a color television image tube

ABSTRACT

A shadow mask support means including three leaf springs for supporting a rectangular shadow mask on a face panel at three sides of a frame of the mask, said three leaf springs having a predetermined relationship with respect to the spring constant and deflection so that, even when the image tube is subjected to a shock load or the shadow mask in thermally expanded, the change in the relative position of the shadow mask and the face panel is minimized.

United States Patent N akamura et a1.

[54] SHADOW MASK SUPPORT MECHANISM FOR A COLOR TELEVISION IMAGE TUBE[72], Inventors: Hiroto Nakamura; Akira Sato, both of Takatsuki;Ken-ichi Doi, Kobe, all of Japan [73] Assignee: Matsushlta ElectronicsCorporation,

Osaka, Japan [22] Filed: March 20, 1970 [21] Appl. No.: 21,422

[30] Foreign Application Priority Data March 24, 1969 Japan ..44/24045[52] U.S. Cl. ..313/85 S, 313/286 [51] Int. Cl. ...H0lj 29/06, HOlj31/20 [58] Field ofSearch ..3l3/85 S, 269

[56] References Cited UNITED STATES PATENTS 3,452,234 6/1969 Lindeman..3l'3/85 S 1 June 20, 1972 3,454,813 7/1969 bewinson ..313/85 S3,449,611 6/1969 Schwartz et aL. ....313/85 S 3,492,522 l/1970 Pappadis..313/85 S 3,524,972 8/1970 Cooper et a1. ..3l3/85 S FOREIGN PATENTS ORAPPLICATXONS 790,713 7/1968 Canada ..313/85 S Primary Examiner-RobertSegal Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT A shadowmask support means including three leaf springs for supporting arectangular shadow mask on a face panel at three sides of a frame of themask, said three leaf springs having a predetermined relationship withrespect to the spring constant and deflection so that, even when theimage tube is subjected to a shock load or the shadow mask in thermallyexpanded, the change in the relative position of the shadow mask and theface panel is minimized.

1 Claim, 5 Drawing Figures PATENTEDJum m2 M M W 4 A. mm m K. 00/

INVENTORS ATTORNEYS SHADOW MASK SUPPORT MECHANISM FOR A COLOR TELEVISIONIMAGE TUBE The present invention relates to a mechanism for stablysupporting a rectangular shadow mask of a color television image tube ona face panel at three points.

In a color television image tube, three shadow leaf springs are normallyused for resiliently supporting a rectangular shadow mask on a facemask. Each of the leaf springs comprises a pin projecting from the innersurface of the side wall of the face panel, and a leaf spring having oneend engaging said pin and the other end secured to the outer surface ofthe side wall of the mask frame. Three such leaf springs are disposedwith suitable spacings in a space between said frame and said facepanel. The spacings of the leaf springs have a great influence on thesupporting characteristics of said mask on said face panel, and in someinstances the leaf springs cannot withstand the shock load applied fromoutside. Further, in some cases, the center of the shadow mask isdisplaced or the mask is rotated about a point at or near the centerthereof when it is thermally expanded.

Therefore, an object of the present invention is to minimize therelative displacement between a face panel and a rectangular shadow masksupported thereon at three points even when the image tube is subjectedto a mechanical shock load or when the shadow mask is thermallyexpanded.

The mask support mechanism of the present invention will now bedescribed with reference to a preferred embodiment shown by way ofexample in the accompanying drawings;

FIG. 1 is a plan view of a mask support mechanism embodying the presentinvention;

FIG. 2 is a detailed view of a portion of the mechanism shown in FIG. 1;

FIGS. 3a and 3b respectively show vector diagrams representing therelative relationship among three spring forces of the leaf springs;

FIG. 4 is a diagrammatical view showing the spring deflection in theleaf spring.

Referring to FIG. 1, a rectangular face panel 1 is combined with a firstleaf spring which is attached to the upper side thereof and which has apin 11 located on the vertical center line Y-Y of the face panel. A leafspring 12 engaging the pin 11 at its one end has a spring portion 13extending from the vertical center line Y-Y toward the right as seen inFIG. 1 and secured at the other end to the outer surface of the sidewall of a frame 2 provided in a rectangular shadow mask 3. Therefore,the spring in the first leaf spring acts along a line 14 whichintersects the vertical center line Y-Y. On the left and right sides ofthe panel, there are disposed a second and a third leaf springs andrespectively which have pins 21 and 31 respectively located on the samehorizontal line X'X'. Springs 22 and 32 which respectively engage withsaid pins 21 and 31 at respective one of their ends have spring portions23 and 33 respectively which extend toward the bottom side of the facepanel 1 and are secured to the frame 2 at their distal ends. The spring22 of the second leaf spring 20 acts along a line 24 which intersects aline 34, along which the third leaf spring 30 acts, at a point on thevertical center line Y-Y. in FIG. 1, the reference X-X shows ahorizontal center line of the face panel 1.

According to the above described three point support mechanism, thedistance by which the horizontal line X'X' is offset from the horizontalcenter line toward the lower side of the face panel has an importanteffect on the shock absorbing characteristics of the mechanism. In thepast, it has been believed that an excellent characteristics will beobtained for withstanding a shock load acting along the image tube axisor a shock load which will be applied on the tube when it is dropped, ifsaid distance is selected to one-fourth of the vertical side length ofthe frame 2.

However, according to the inventors, it has been found that, when thespring portions 23 and 33 of the second and the third leaf springs 20and 30 are arranged so as to intersect a horizontal line X"X' which islocated below the horizontal center line X-X and spaced therefrom by adistance equal to one-fourth the vertical side length of the frame, themost ex- 4 cellent shock absorbing characteristics can be obtained.

Further, in addition to the above described locations of the three leafsprings 10, 20 and 30, the direction and the amount of the spring forcesacting along the lines 14, 24 and 34 are also important. Assuming thatidentical leaf springs are used in the mask support mechanism and thespring of each leaf springs develops a spring force of F kg, the springforces can be represented as in FIG. 3a. These forces will produce aresultant force shown by the reference T and a resultant moment shown byR in FIG. 3b, both the resultant force and moment being applied to theshadow mask 3. These forces will cause a temporary or permanentdeviation of the location of the mask 3 when the temperature of the mask3 is increased, with the result that the color purity of the image tubewill be adversely affected.

The present invention aims at eliminating said undesirable deviation ofthe mask location, while at the same time, obtaining a sufficient shockabsorbing effect.

When the second and the third leaf springs 20 and 30 having springs of Fkg are arranged with the angle 0 in FIG. 2 selected to a nominal valueof 714 and the spring force of the first leaf springs 10 is determinedto about 0.25 F kg which is equal to 2 F sin 714 the spring forces ofthe three leaf springs are substantially balanced and the resultantforce T and the moment R can be reduced to a minimum value. The springof the first leaf springs 10 may be designed to have a spring force of0.25 F kg by reducing the spring constant (ln an elastic system obeyingthe Hooke law, the magnitude of the applied force F, and the elongationx are related by F kx, where the constant k is called the springconstant; i.e. spring constant force/deflection force/elongation). Thisdesign may be effective to minimize said deviation of the thermallyexpanded mask. However, if the spring constant of the first leaf springs10 is reduced by for example simply reducing the cross-section of thespring, the supporter will become too weak to withstand a shock loadwhich may be applied to the tube when it is dropped. The presentinvention has been accomplished by noting the fact that the spring forceis the product of the spring constant and the deflection and ischaracterized by the fact that both the spring constant and thedeflection are changed to obtain a spring force of 0.25 F.

In FIG. 2, the distance a between the horizontal center line X--X andthe horizontal line XX' may be 54 mm for a 20 inch size rectangularimage tube. ln this case, in order to make the first leaf springs 10withstandable to the shock load in the direction of the tube axis, itsspring constant must be about 60 percent of those of the second and thethird leaf springs 20 and 30. Further, for image tubes of average sizeincluding those of 22 inch size, the spring constant of the first leafsprings may be selected to 50 to 60 percent of those of the second andthe third leaf springs.

In the mask support mechanism in accordance with the present invention,the spring constant of the first leaf springs 10 is selected to be 50 to60 percent of those of the second and the third leaf springs 20 and 30and,, at the same time, the deflection of the spring, that is, thedistance b shown in FIG. 4 in the first leaf springs 10 is reduced ascompared with those of the other leaf springs 20 and 30 so that theeffective spring force of the first leaf springs 10 is reducedsubstantially to 0.25 F kg. The spring deflection in the first leafsprings may be about 0.42 to 0.5 of those in the second and the thirdleaf springs and, by this arrangement, both the thermal characteristicsand the shock absorbing characteristics of the mechanism for mountingthe shadow mask on the face panel are highly improved.

What is claimed is:

l. A mask support mechanism for a color television image tube includinga rectangular shadow mask supported on a rectangular face panel, saidmechanism comprising a first leaf spring, one distal end of said springengaging a pin provided on the upper side of said rectangular face paneland providing a spring portion extending from. a vertical center linetoward one side only of said panel and secured at the other end to theouter surface of the side wall of a frame provided in said rectangularshadow mask, and a second and a third substantially identical leafsprings having ends engaging pins provided on the left and right sidesof said panel, and each other end of said first, second and thirdsprings being secured to the outer surface of the side wall of a frameprovided in a rectangular shadow mask, a horizontal line connecting thespring portions of said second and third leaf springs being spaced fromthe horizontal center line of said face panel by a distance equal toone-fourth the shorter side length of the shadow mask frame, said shadowmask being resiliently supported at the inner side of said panel, thespring constant of said first leaf spring being selected to be 50 to 60percent of those of the second and the third leaf springs and the springdeflection of the first leaf spring being determined to be small ascompared with those of said second and third leaf springs, so that inthe case of thermal expansion of the shadow mask the resultant force ofthe spring forces of said first, second and third leaf springs issubstantially reduced.

III I! i

1. A mask support mechanism for a color television image tube includinga rectangular shadow mask supported on a rectangular face panel, saidmechanism comprising a first leaf spring, one distal end of said springengaging a pin provided on the upper side of said rectangular face paneland providing a spring portion extending from a vertical center linetoward one side only of said panel and secured at the other end to theouter surface of the side wall of a frame provided in said rectangularshadow mask, and a second and a third substantially identical leafsprings having ends engaging pins provided on the left and right sidesof said panel, and each other end of said first, second and thirdsprings being secured to the outer surface of the side wall of a frameprovided in a rectangular shadow mask, a horizontal line connecting thespring portions of said second and third leaf springs being spaced fromthe horizontal center line of said face panel by a distance equal toone-fourth the shorter side length of the shadow mask frame, said shadowmask being resiliently supported at the inner side of said panel, thespring constant of said first leaf spring being selected to be 50 to 60percent of those of the second and the third leaf springs and the springdeflection of the first leaf spring being determined to be small ascompared with those of said second and third leaf springs, so that inthe case of thermal expansion of the shadow mask the resultant force ofthe spring forces of said first, second and third leaf springs issubstantially reduced.